1. Field of the Invention
The present invention relates to a musical tone synthesizing apparatus which synthesizes musical tones of plucked stringed instruments, struck string instruments and the like.
2. Prior Art
Devices are well known wherein, by activating the simulation model of the tone generation mechanisms of an acoustic musical instrument, sound of the acoustic musical instruments can be artificially synthesized.
As an example, there is known device which synthesizes the sound of struck string instruments such as an acoustic piano by the configuration containing a low-pass filter for simulating reverberation losses in the strings and a delay circuit for simulating propagation delays of the vibration of the strings, wherein the low-pass filter and delay circuit are connected together so as to form a closed-loop circuit. With such a device, an excitation signal (e.g., an impulse signal) is introduced into the closed-loop circuit. Thus, the introduced impulse excitation signal circulates through the closed-loop circuit once with a period identical to the period in which the vibration reciprocates through the string once. The signal circulating through the closed-loop circuit is subjected to the bandwidth restriction each time it traverses the low-pass filter. Then, the circulating signal is picked up from the closed-loop circuit as a musical tone signal.
In this case, the above-mentioned excitation signal such as impulse signal is supplied by an excitation circuit which is provided to simulate the influence of the hammer striking the strings. This excitation circuit calculates the relative displacement relationship between the strings and hammer based on the weight of hammer, the initial velocity of hammer and the circulation signal circulating in the closed-loop circuit. Then, it computes the repulsive force to be given to the hammer from the string based on the relative displacement, and finally supplies the signal representing the repulsive force to the closed-loop circuit. Furthermore, in the excitation circuit, the repulsive force is set as a control parameter which is used for calculating the relative displacement between the strings and hammer to be occurred in the next stage.
Incidentally, this type of musical tone synthesizing apparatus is disclosed in Japanese Patent Laid-open Publication No. 63-40199.
In the conventional musical tone synthesizing apparatuses described above, the excitation circuit is in the form of loop-form circuit. Therefore, in the case where the foregoing control parameter is merely changed, the digital computation may be in the overflow state when computing the relative displacement. Thus, control stability of the excitation circuit cannot be obtained.
Accordingly, the conventional musical tone synthesizing apparatus is disadvantageous in that it is difficult to find out the suitable value for the control parameter in the case where the control state and control parameters of the excitation circuit are to be varied. Thus, it is extremely difficult to vary the value of control parameter.